'Although it is not true that all conservatives are stupid people, it is true that most stupid people are conservative," according to John Stuart Mill. David Willetts - "Two brains Willetts", in newspaper shorthand - would doubtless disagree. But the shadow education secretary is currently trying, valiantly, to force his party to cast its mind back to Mill's day in order to rediscover a coherent philosophy.

In a series of speeches to the faithful, he is invoking the names of Disraeli and, in fact, Mill, urging Conservatives to go back to the future. The message for the party, he insists, is to be found in its past.

"What we don't have," says Willetts, "is a history of what Conservatives have thought, and why. What I'm trying to do is capture the cast of mind of conservatism - what Conservatives, for example, thought they were doing in the 19th century and to establish the historical fact that modernising is a Conservative tradition."

One of the key terms in Willetts's recent lectures has been "principle". How, precisely, is that different from "ideology" or "policy"?

"The crucial difference is that ideology comes from a kind of canonical text, or set of texts, and one of the great things about conservatism is that there are no canonical texts. I remember a conversation with the late Sir Denis Thatcher, after our 1997 landslide defeat. I asked him for advice on what we should do. His reply was simple: 'Get back to basic Conservative principles.' And then he added: 'But don't ask me what they are.'"

I'll ask you. What are these principles?

"For me, there are two key principles. Or, to put it another way, there are two key emotions that people feel in modern Britain. One is the value of personal freedom, of personal choice, of trust in other people and a wariness about the state's ability to make us good, or the state's ability to solve problems. All this tends towards an empowering of the individual. Secondly - this is the bit which is much harder to express - there's a belief, or an understanding, that there is more to life than an individual's acts of consumption and choice strung together. An understanding that you have ties to your family, ties to your neighbourhood, ties to your society. An understanding that you have obligations, and that public service matters.

One of the problems that our party has is that the second strand of conservatism was, traditionally, not expressed but simply practised - because it came from the institutions with which Conservatives were then associated. Fifty years ago, most Tory MPs had served in the armed forces and had the obligations of the officer - that the men eat before you do, for example. Or they were landed gentry who had a traditional view of their obligations to people in the countryside around them. They were, in general, linked to the Church of England. So the ideal of public service was embodied in the institutions with which we were associated, as a party. Those institutions have eroded and our connections with them have weakened. We've neither been very good at expressing that part of conservatism, nor are we any longer as firmly linked with institutions that embody those principles."

How did the Tories come to lose their connections with those principles?

"When we came to power in 1979, Britain's problems were above all economic, and the country needed a dose of free-market medicine. And by and large, I think in those 18 years of Conservative rule we did an enormous amount to tackle Britain's economic problems. But that meant that, in the eyes of the electorate, and perhaps also in those of many people working within the party as committed Conservatives, we ended up as 'the economics party'. What we had lost sight of was the other half of the Conservative tradition: which is the language of community, of obligation, of roots. And I sometimes say to my friends and colleagues: if you're going on the Today programme tomorrow morning to explain why you need to hold down levels of public spending and tax, or why the burden of regulation or red tape is too high, we all know exactly what to say. But if you go on the Today programme tomorrow and talk about how, say, the family is changing, and what that means for opportunities for children, or the extent to which faith schools should be publicly funded, or what it is that's the shared culture of our country that you have to participate in to be the recipient of public money - then there's a whole mass of different views and that's what people are now hungry to hear from us about. And we don't necessarily have the ready answers."

Willetts says he realised that particular shortcoming in modern Conservative thought as a result of his own personal experience. As a young man he was a libertarian, "but when you get older - particularly when you have kids - you suddenly start thinking, 'Well, I don't actually want drugs being traded outside the school gates. I do care about what's broadcast on TV. I do worry about the kind of society my children are going to live in. I do worry about the environment, because, long after I've gone, I don't want to feel that the Arctic ice cap is melting and that half of Britain is flooded.' Someone described a libertarian as being someone in favour of childless immortals. My personal and autobiographical definition of conservatism is a free marketeer with children."

In prescribing a period of fruitful meditation for his party, Willetts has repeatedly returned to an era of internal strife and crisis: the 1840s, when the party was torn apart by the conflict between the "Young Englandism" of Disraeli and the backwoods Toryism of Peel. Are the current mutterings of the Tory right about David Cameron's attempts to change the party a repeat of that process?

"Any party that has a sense of history and wants to hold on to what is best in the country inevitably runs the risk of losing touch with the society around it. And you couldcertainly interpret the history of conservatism as a series of moments - as in the 1840s, and in 1906, and in 1945 - when the party's absolutely understandable reverence for tradition has left it disconnected from contemporary Britain. And there is then a crisis in which the party has to remake itself and catch up with the society around it.

"After 1906 we made a mess of it, and the mistakes we have made since 1997 are, in many ways, like those we made after 1906. There is an argument that this is a process the party goes through at certain periods in its history. That's why 'modernising' - I don't particularly like the term - is genuinely a Conservative tradition".